Major losses for the Democrats in November’s mid-term elections are widely expected, with Republicans predicted to recapture at least the House of Representatives. No matter what the final tally is, instant analysis will proclaim that American politics has been transformed by the Tea Party movement. But the instant analysis will be wrong.

New American political movements come in two varieties: genuine third-party movements and those that just mobilise the base of one of the existing parties. The former transforms an existing party system; the latter reinforces it. And the Tea Party is an example of the latter – so while it has attracted a great deal of attention, it has little long-term potential to transform America’s political landscape.

America’s stable two-party structure flows from an electoral system, inherited from Britain, with a built-in bias against third parties. Such parties, when they do occur, are often short-lived vehicles that introduce a new issue or ideology, fading away once one of the major parties has co-opted its concerns. In the words of the historian Richard Hofstadter, “Third parties are like bees; once they have stung, they die.”

Insurgent ideological movements, such as the Tea Party, can play the same role. The conservative movement won the Republican nomination for its standard-bearer, Barry Goldwater, in 1964. In the same way members of the antiwar, culturally liberal new politics movement triumphed in mid-term elections in 1974, following the defeat of George McGovern in 1972. Crucially, whether organised as third parties or insurgents, such factions go on to transform one of the two parties, and thus the political system.

But movements that only mobilise the base of a party do not have that effect. Instead, they increase turnout, and thus may shift control of the government. This is what happened when the Republicans last won a significant mid-term victory in 1994, under the leadership of Newt Gingrich. That win marked an advance for the Goldwater-Reagan right but not a new departure. Democratic victories in 2006 and 2008 also benefited from the passion of Democratic partisans.

In the same way the Tea Party represents an energised Republican base. There is a high degree of overlap between those who say they identify with it and conservative Republicans. Polling in September, for instance, found that 71 per cent of Republican voters now support the movement. Elsewhere the movement has been backed by conservative media, while its icons – from Kentucky senate candidate Rand Paul to potential Republican presidential nominee Sarah Palin – are conservatives or libertarians, rather than genuine populists. Its denunciations of big government and high taxes are also indistinguishable from mainstream conservatism.

In short, the Tea Party is best thought of as an energetic revival of Goldwater-Reagan conservatism. Its adherents are angry for the same reason that Democrats were angry between 2001 and 2007: their party is out of power. There is a persistent tendency in the commentariat to get this wrong, by casting the Tea Party as pitchfork-yielding populists at war with elites of all kinds. Indeed, it is often asserted that economic downturns produce waves of populism. But the Tea Party does not fit the profile, even if, like all partisan movements outside of power, it employs anti-establishment rhetoric. Polls show its sympathisers are more wealthy and educated than most Americans. Their decision to make the government – rather than Wall Street – the object of their anger would also be inexplicable if they were a genuine populist movement.

The result is that in the near term, the Tea Party’s potential to reshape the political landscape will come only from imposing a new orthodoxy within the Republican party. The expected Republican majorities in the House will be even more opposed to tax increases and further stimulus spending between November’s mid-term election and the presidential election in 2012. Congress will be more polarised and more paralysed. The movement may also impose new litmus tests on candidates who aspire to the Republican presidential nomination. Already Indiana governor Mitch Daniels, widely considered a possible candidate, is under attack for suggesting the need to consider either a value added tax or a gasoline tax to deal with the budget deficit.

If slow growth and mass unemployment persist, genuinely novel forces may arise to shake up American politics. But not this year. In the long run the Tea Party is likely to fade into demoralisation and recrimination, as its anti-statist ideology collides with the realities of 21st-century big government. In time it may even be viewed as the last gasp of Goldwater-Reagan conservatism. The coming gains will bring dramatic changes in policy and personnel. However, to interpret them as evidence of a lasting realignment will be to misinterpret, as political climate change, what is only a tempest in a Tea Party.